1. Field of the Invention
This invention relates to microwave amplifier systems and, more particularly, to a microwave amplifier subsystem useful to provide dual mode operation in an electronic counter-measures system.
2. Description of the Prior Art
Heretofore various electronic countermeasures systems have been used for protecting aircraft by defeating or deceiving radar systems, the now conventional and well known means used to electronically detect and determine the position, altitude, etc. of flying aircraft. Present day counter-measures systems perform this function in either two ways, as has been reported in newspaper and other publicly available literature. In one, a generator of broad spectrum continuous wave microwave energy is operated which generates continuous electronic "noise". This noise is picked up by the offending radar and is added to the ambient electronic "background signals", the normal "noise", received by the radar. To detect an intruding aircraft in the normal operation of the radar, the radar transmits synchronized pulses and the operator must observe the "echo", the electromagnetic energy pulse reflected by the intruding aircraft. A high level of noise "masks" or clutters the pulses as may be relfected from such approaching aircraft and the radar is unable to detect its presence. At some position of the approaching aircraft, however, the radar echo becomes large enough in magnitude to exceed the electronically generated jamming noise and the echo is detected. At this position the approaching aircraft is electronically visible.
As is apparent, if the power level of the electronic noise source could be infinitely large, the radar system is permanently defeated and the approaching aircraft would always appear electronically "hidden". In practice the electronic noise sources are limited to state of the art power levels. Thus at some position of approach, in part depending upon the power generated by the countermeasures noise source, the approaching aircraft becomes electronically "visible" and a second countermeasures system carried by the aircraft must be placed into operation if that aircraft is to remain protected. The second electronic countermeasures equipment in the aircraft detects incidence of an electronic signal from the offending radar station and thereupon transmits a "false" echo. This false echo is sufficiently greater in power and predominates over the "real" echo. The false echo represents false information and the offending radar installation makes an incorrect determination of the position of the approaching aircraft. Thus any anti-aircraft missiles launched relying upon the radar information are misdirected. In countermeasures terminology, the operation of equipment to generate continuous noise is referred to as "CW mode" operation and the operation of such equipment to transmit false pulses is referred to frequently as the "pulse mode".
To that end a small sized lightweight countermeasures system to be carried by each individual aircraft having capability for operation in both of the aforecited "modes" of operation, sometimes referred to as "dual mode" capability, is a desirable protective device. One of the critical components of present day countermeasures equipment is the traveling wave tube, a microwave tube which amplifies microwave frequency signals. A first known approach to this requirement uses a single traveling wave tube capable of operation in both the CW mode and in the pulse mode. This approach obviously reduces weight and volume of countermeasures equipment to a minimum, however, performance is limited in regard to that desired.
A second known approach employs two traveling wave tubes: a first traveling wave tube designed for and operated in the continuous wave mode which feeds the CW energy into a second traveling wave tube. The second traveling wave tube is especially designed for two purposes: (1) to provide a high power pulse output signal when the system is placed in the pulse mode, and (2) to be electronically transparent, much as a window, to CW microwave signals from the first tube when the system is operating in the continuous wave mode. It is apparent that if the first tube in such a system fails in service, both the CW and pulse mode counter-measures capability fails, whereas if the second tube fails there may only be remaining the CW mode counter-measures capability.
A third method uses pulse and continuous wave traveling wave tubes followed by a hybrid junction to combine power. Disadvantages in this approach include the fact that if a single antenna is to be driven, roughly one-half of the power is lost in the combiner, or if fore and aft antennas are driven by the two hybrid output ports, phase will necessarily be dissimilar in the antennas depending on the mode of operation.